Hitherto, it has been demanded to transmit video and audio data with least delay in, for example, communication systems using video and audio, such as bidirectional video conference systems, and in mixed systems with a non-compression environment in broadcasting stations or the like. In recent years in particular, the amount of data has been increasing as the quality of video and audio has been improved, and accordingly, data transmission with further reduced delay has been demanded.
For example, in MPEG (Moving Picture Experts Group) and H.26x compression systems, the compression ratio has been increased based on motion prediction. When motion prediction is performed, the algorithm becomes complicated, and the processing time involved increases in proportion to the square of the frame size. In principle, a coding delay of a few frames occurs. When bidirectional real-time communication is to be performed, the delay time becomes almost an allowable delay time of 250 ms, which is a length that is not negligible.
Also, intraframe codecs represented by JPEG (Joint Photographic Experts Group) 2000 do not use interframe difference information. Thus, the above-described delay does not occur. However, since compression is done on a frame-by-frame basis, the codec must wait at least one frame before the start of encoding. Since current general systems employ 30 frames per second in many cases, a waiting time of about 16 ms is necessary before the start of encoding.
Therefore, it has been demanded to further reduce this delay, and a reduction of delay in portions other than encoding and decoding, such as in a packetizing process and a depacketizing process, has become necessary as well. For example, a method of reducing the capacity of a buffer memory has been conceived to reduce transmission delay (for example, see Patent Citation 1).
Now, it frequently occurs that transmission errors occur in a communication process in digital video communication of transmitting video and audio data and affect the quality of reproduction.
Patent Citation 1: Japanese Unexamined Patent Application Publication No. 2005-12753